Electronic control systems, so-called "on-board computers", are frequently used in automative vehicles; one such computer is described in German Patent Disclosure Document DE-OS No. 26 55 948 to which U.S. Pat. No. 4,174,688 corresponds, directed to a computer to calculate the proper timing of the ignition instant of an external ignition system, and the control of current flow through one or more ignition coils. Many types of motor vehicles use, also, other electronic apparatus which control various features of the power drive train, for example which are arranged to sense engine knocking, control injection of fuel, and the like, and derive electrical signals which are fed to the on-board vehicular computer. The vehicular computer customarily cooperates with a transducer, for example an optical, magnetic, or similar transducer, which has a part rotating in synchronism with the engine, and is electrically connected to a trigger circuit to which, in turn, a digital network is connected, which forms part or all of the computer, to calculate the time of initiation of current flow through an ignition coil and the time of interruption of current flow, and hence the ignition instant. The signal processing is analog/digital/analog, that is, the transducer and trigger circuit provide analog signals respectively representative of the rotation of the engine, and the output circuit likewise is an analog circuit which controls the current flow through the ignition coil. Intermediate calculating steps are carried out by a digitally operating microprocessor. Such systems, particularly when applied to ignition systems which calculate the dwell angle in a digital microprocessor are sensitive to operating voltage, that is, to voltage below a predetermined minimum operating level. If the voltage of the network drops below the minimum level, some or all of the networks of the digital microprocessor no longer operate as designed and intended, which may result in erroneous signals being applied to the analog output stages, and hence storage of electromagnetic energy under erroneous condition and triggering of sparks at uncontrolled random time instants.